Production of high octane gasoline

ABSTRACT

A process for producing a gasoline which includes the following steps: A. SEPARATING A NAPHTHA FEEDSTOCK WHICH CONTAINS ISO-C6 and normal C6 paraffins into a light fraction containing at least one-half of the total iso-C6 paraffins and a heavy fraction containing at least 60 percent of the normal C6 paraffin, B. CATALYTICALLY REFORMING THE HEAVY FRACTION TO OBTAIN REFORMATE, AND C. BLENDING AT LEAST A PORTION OF THE LIGHT FRACTION WITH THE REFORMATE TO OBTAIN GASOLINE OR GASOLINE BLENDING STOCK. The splitting or separating of the naphtha feedstock as per step (a) is preferably carried out by distillation, for example in a deisohexanizer, with the cut point between the light and heavy fractions being at about 150*F. and with the light fraction being rich in iso-C6 paraffins and the heavy fraction rich in normal C6 paraffin.

United States Patent [191 Hughes et al.

[111 3,821,104' June 28, 1974 1 PRODUCTION OF HIGH OCTANE GASOLINE Primary Examiner-Herbert Levine 751 Inventors: Thomas R. Hughes, Orinda; Robert g f ggjg Magdeburger R L. Jacobson, Pinole; Richard C. g Robinson, San Rafael, all of Calif. AB 7 T [73] Assignee: Chevron Research Company, San [57] STRAC Francisco, Calif A process for producmg a gasoline which includes the following steps: [22] Flledi May 1972 a. separating a naphtha feedstock which contains [21] AppL NO; 257,891 iso-C and normal C paraffins into a light fraction 7 containing at least one-half of the total iso-C Related Apphcatlon Data paraffins and a heavy fraction containing at least [63] Continuation-impart of Ser. No. 154,521, June 18, 60 percent Of the normal C paraffin,

I971, abandoned. b. catalytically reforming the heavy fraction to obtain reformate, and Cl n 7, 208/ 141, c. blending at least a portion of the light fraction 4 i /3 0 with the reformate to obtain gasoline or gasoline [51 hit. CI Cl0g 35/04 blending stock, 7 [58] Fleld of Search 208/93, 141 l7 The Splitting or Separating f h naphtha feedstock as per step (a) is preferably carried out by distillation, [56] References C'ted for example in a deisohexanizer, with the cut point be- UNITED STATES PATENTS tween the light and heavy fractions being at about 2.937.133 5/l960 Herrmann et ai 208/80 ISOOF- and with the light fraction being rich in s 2938.936 5/1960 Belden 208/93 paraffins and the heavy fraction rich in normal C 2946,736 7/l960 Muffat ct al. 208/65 paraffin. 3,003,949 Y lO/l96l Hamilton 208/93 3,069,349 12/1962 Meiners 208/85 8 Clams, 5 Drawing Flgures SEPARA'LION 3 3 I" 6 l g 6 T.E.R, z 1 H2 9 I g I c c4 2 so 4so F. l 2 g l E l w i U l 6 5 l l, CATALYTlC E RE FORMER 5 L J OVERALL BLEND YIELD, LV 7 BASED UN UNSPLIT NAPHTHA FEEDSTOCK PATENTEDJu'n'm mm SHEEI 10F 3 l l I 78 8O 82 84 86 88 OVERALL BLEND OCTANE, F-1 CLEAR FIG.1

1 PRODUCTION OF HIGH OCTANE GASOLINE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 154,521, filed June 18, 1971 and now abandoned.

BACKGROUND OF THE INVENTION 1. Field The present invention is concerned with producing a gasoline or gasoline blending stock having increased octane.

2. Prior Art It is common in the prior art to separate a full boiling range naphtha for example a naphtha boiling from about 80F. to about 450F., into a light fraction and a heavy fraction, to reform the heavy fraction only, and then to combine the reformate with the light fraction to form a gasoline or gasoline blending stock. When the separation of the light fraction and the heavy fraction takes place in a typical distillation column, it is common to perform the distillation with a cut point of about 180F., although both somewhat lower and somewhat higher cut points are sometimes used.

It is further known in the prior art to separate a 150F. 185F. fraction rich in methylcyclopentane and cyclohexane from high naphthene content naphthas, to process the 150F. 185F. fraction to form benzene, to reform the 185F. fraction from the naphtha to form gasoline and to include with the gasoline materials from the naphtha which boil below 150F. Such a process is described, for example, in US. Pat. No. 2,689,208.

Recently patents have issued directed to production of lead-free gasoline by combination processes based largely on reforming. For example, US. Pat. No. 3,649.520 discloses a method for upgrading gasoline boiling range hydrocarbons by an overall process which includes dehexanizing a naphtha feedstock to obtain a C fraction which is fed to a catalytic reformer. The overhead from the dehexanizer contains substantially all of the normal hexane as well as the isohexane. The dehexanizer overhead is further distilled to remove C and C paraffins and then fed to a reforming zone. Thus, U.S. Pat. No. 3,649,520 does not contemplate separating an iso-C paraffin-rich stream from naphtha and then feeding a stream rich in normal Cg, paraffin to catalytic reforming.

US. Pat. No. 3,658,690 discloses another combination process for upgrading gasoline boiling range material. The overall process disclosed in this patent includes depentanizing a naphtha feedstock and then feeding an iso-C,,+ paraffin stream to reforming. Thus, US. Pat. No. 3,658,690 does not contemplate separating an iso-C paraffin-rich stream from naphtha and then feeding a stream rich in normal C paraffin to eatalytic reforming.

Parenthetically, it can be mentioned that terminology such as iso-C means a feedstock boiling from the range of iso-C upward to include substantial higher boiling hydrocarbons, i.e. the iso-C represents the lower point of the boiling range of the hydrocarbon fraction.

SUMMARY or THE INVENTION According to the present invention a process is provided for producing a gasoline which comprises:

a. separating a naphtha feedstock which contains iso-C and normal C parafiins into a light fraction containing at least one-half of the total iso-C,

paraffins and a heavy fraction containing at least 60 percent of the normal C paraffin,

b. catalytically reforming the heavy fraction to obtain I naphtha derived from a typical Arabian crude oil..

Thus, preferred feed stocks for the process of the present invention contain at least 3 volume percent normal C paraffin and at least 1 volume percent iso-C parafiins, and more preferably 6 volume percent or more normal C paraffin and 2 volume percent or more iso-C paraflins.

Preferably the separation of the naphtha feedstock as per step (a) above is carried out so that the heavy fraction has an iso-C lparafiin to normal C paraffin ratio about one-third or less of the thermodynamic equilibrium ratio under the conditions in the reforming zone, and the light fraction has an iso-C paraffin to normal C paraffin ratio more than about two-thirds of the thermodynamic equilibrium ratio under the conditions in the reforming zone.

Among other factors the present invention is based on our finding that the present process results in a surprisingly high overall yield of a given octane gasoline product. Specifically, a high yield compared to reforming a conventional reformer feedstock for production of gasoline followed by blending the reformate with unreforrned C light fraction. A conventional feedstock" is used herein to mean a reforming feedstock which is not based on a sharp cut between iso-C paraffms and normal C paraffin. For example, a conventional reformingfeedstock. may boil from 180F.

upwards. The present invention in general contemplates that the naphtha feedstock is cut at about F. to provide a l50F.+ feedstock for reforming, and also that the reformer feed be prepared by separating out an isohexane-rich stream and leaving a normal hexanerich stream which boils from'about l50F. ,upwards as the specific reformer feed.

In the process of the present invention generally the light fraction is directly blended with the reformate. However, there can be steps applied to either or both the light fraction and the reformate before blending, such as isomerization and/or various distillation steps. But, it is essential in the present invention to blend at least a portion of the reformate which remains after any additional steps with at least a portion of the iso-C paraffin-rich stream remaining after any additional steps. As illustrative of additional steps that might be applied, reference can be made to the previously mentioned US. Pat. Nos. 3,649,520 and 3,658,690. Note, however, that-these patents at least in part teach contrary to the present invention because in view of these patents one would conclude that a split between iso-C and normal C paraffins is not an especially advantageous split for obtaining reformer feed. Instead from these patents one would conclude that a C (-180F.+) is a desirable cut point (US. Pat. No. 3,649,520) or that iso-C -l- (-l lF.+) is a desirable cut point (US. Pat. No. 3,658,690) upon which to base the reformer feed. This is in general accord with the prior art", that is, the prior art does not enable one to select a cut point between iso-C and normal C paraffins as a particularly advantageous cut compared to other out points. Whereas, the research work pursuant to the present invention shows the especially advantageous overall blend yield at a given octane when basing the reformer feed on a cut between iso-C and normal C followed by feeding the normal C -rich fraction to re forming and then blending the iso-C rich fraction with the reformate.

The term reformate is used to connote a reforming unit product which has been stabilized, for example, by removing at least a portion of the butanes and lighter material from the reforming unit effluent stream.

DISCUSSION OF SOME SPECIFIC EMBODIMENTS OF THE INVENTION l. One embodiment of the invention is an improvement in a process for producing a gasoline or gasoline blending stock from a naphtha feedstock boiling within the range from about 80F. to about 450F. by steps including separating said feestock in a distillation zone into a light isoparaffin enriched fraction and a heavy fraction, catalytically reforming said heavy fraction in a reforming zone at reforming conditions in the presence of hydrogen and a reforming catalyst, and blending the reformate so obtained with the light fraction to produce the gasoline or gasoline blending stock.

The improvement comprises selecting as the naphtha feedstock a naphtha feedstock having a total C paraffin content of at least 4 volume percent, a normal C paraffin content of at least 3 volume percent, and a ratio of iso-C paraffins to normal C paraffin within the range from about 1/3 to about 3/1. The improvement further comprises operating a distillation zone at a cut point which falls within the range from about l45F. to about 155F. under conditions efficaceous to produce the light isoparaffin enriched fraction boiling within the range from about 80 F. to about 155F., having at least one-half the total iso-C paraffins from the naphtha feedstock and preferably having a ratio of iso-C paraffins to normal C paraffin above the thermodynamic equilibrium ratio of iso-C paraffins to normal C paraffin under the conditions of the reforming zone, and to produce the heavy fraction which boils within the range from about l45F.to about 450 F. having a ratio of iso-C paraffins to normal C paraffin below the thermodynamic equilibrium ratio of iso-C paraffins to normal C 6 paraffin under the conditions of the reforming zone and having at least 60 percent of the total normal C, paraffin from said naphtha feedstock and recovering an increased octane gasoline or gasoline blending stock product.

PREFERRED EMBODIMENTS WITH INCORPORATED ADSORPTION (ll-V) ll. Another embodiment of the invention is a process for producing a gasoline product of increased octane from a naphtha feedstock boiling within the range from about 80F to about 45 0F. and having a total C paraffin content of at least about 4 percent a normal C paraffin content of at least about 3 percent, and a ratio of iso-C paraffins to normal C paraffin within the range from about l/3 to about 3/1.

The process comprises separating the naptha feedstock by rough distillation with low degree of separation into a first fraction boiling within the range from about F. to about F. and a second fraction boiling within the range from about 1 45F to about 450F.

The first fraction is contacted in an adsorption zone with an adsorbent that selectively adsorbs normal C and normal C paraffins without significantly adsorbing iso-C paraffins, isoC paraffins, naphthenes or benzene. A light isoparaffin enriched fraction is recovered from the adsorption zone, said light isoparaffin enriched fraction comprising said iso-C paraffins, iso-C paraffins, naphthenes and benzene, if present, and said light isoparaffin enriched fraction having a ratio of iso-C paraffins to normal C paraffin above the thermodynamic equilibrium ratio of iso-C paraffins to normal C paraffin under the conditions of the catalytic reforming of a heavy fractionand having at least one-half half of the total iso-C paraffins from the naphtha feedstock.

A normal C paraffinand normal C paraffin-enriched stream is removed from a zone of the selective adsorbent and the contactingof the first fraction with that zone of the selective adsorbent is recommenced. A heavy fraction, comprising said second fraction and said normal C paraffinand normal C paraffin-enriched stream removed from said selective adsorbent and having at least 60 percent, on the average, of the total normal C paraffin from said naphtha feedstock is contacted with hydrogen and a reforming catalyst at reforming conditions in a reforming zone, said heavy fraction further having a ratio of iso-C paraffins to normal C paraffin substantially below the I thermodynamic equilibrium ratio of iso-C paraffins to normal C paraffin under the conditions of the reforming zone. The reformate is then combined with the light isoparaffin enriched fraction to produce the product of 1 increased octane number. III. Yet another embodiment of the present invention is a process for producing gasoline of increased octane number from a naphtha feedstock boiling'within the range from about 80F. to about 450F. and having a total C paraffin content of at least about 4 percent, a normal C paraffin content of at least about 3 percent, and a ratio of iso-C paraffins to normal C paraffin within the range from about 1/3 to about 3/1.

The process comprises separating the naphtha feedstock by rough distillation into a first fraction boiling within the range from about 80 F. to about 170F. and a second fraction boiling within the range from about l45F. to about 450F.

The firstfraction is contacted with an adsorbent selective for adsorbing normal C paraffin and normal C paraffin in at least one of a plurality of selective adsorption zones. A light isoparaffin enriched fraction, as described above, is recovered, said light isoparafiin enriched fraction having a ratio of iso-C paraffins to normal C parafiin above the thermodynamic equilibrium ratio under the reforming zone conditions used for reforming a heavy fraction and having at least one-half of the total iso-C parafiins. The light isoparaffin enriched fraction is recovered from the contacting in at least one of a plurality of selective adsorption zones The contacting of the first fraction with the selective adsorbent is periodically discontinued when the ratio of iso-C paraffins to normal C paraffin in said light isoparaffin enriched fraction approaches or falls below the thermodynamic equilibrium ratio under the conditions of catalytic reforming of a heavy fraction as set out below. Thereafter or substantially simultaneously with the periodic discontinuing, the first fraction is contacted with the selective adsorbent in at least one other of said plurality of selective adsorption zones. A light isoparaffin enriched fraction is recovered from the contacting in said other selective adsorption zone, said light isoparaffin enriched fraction being as set out above.

A normal C paraffin and normal CGParaffin stream is removed from said selective adsorbent in at least one of a plurality of selective adsorption zones which is no longer efficiently adsorbing normal C paraffin and normal C paraffin. A heavy fraction, comprising said second fraction and a normal C paraffinand normal C paraffin-enriched stream removed from said selective adsorption zone and having at least 60 percent, on the average, of the total normal C paraffin from said naphtha feedstock, is contacted with hydrogen and a reforming catalyst in a reforming zone at reforming conditions. The reformate is combined with the light isoparaffin enriched fraction obtained from the plurality of selective adsorption zones to produce the product of increased octane number.

lV. Still another embodiment of the present invention is a process for producing gasoline of increased octane number from a naphtha feedstock boiling within the range from about l 10F. to about 450F. (a depentanized naphtha) and having a total C paraffin content of at least about 4 percent, a normal C paraffin content of at least about 3 percent, and a ratio of isoparaf fins to normal C paraffin within the range from about 1/3 to about 3/1 The process comprises separating the naphtha feedstock by rough distillation into a first fraction boiling within the range from about 110F. to about 170F. and a second fraction boiling within the range from about 145F. to about 450F., i.e., using a cut point within the range from about 145F. to about 170F.

The first fraction is contacted in an adsorption zone with an adsorbent thatselectively adsorbs normal C paraffin without significantly adsorbing iso-C fraction and saidnormal C paraffin enriched stream removed from said selective adsorbent, said heavy fraction having at least 60 percent, on the average, of the total C paraffin from said naphtha feedstock, and said heavy fraction further having a ratio of iso-C paraffins to normal C paraffin substantially below the thermodynamic equilibrium ratio of iso-Q; paraffins to normal C paraffin under the conditions of the reforming zone, is contacted with hydrogen and a reforming catalyst at reforming conditions in a reforming zone. The reformate is then combined with the light isoparaffin enriched fraction to produce the product of increased octane number.

V. Another embodiment yet of the present invention is a process for producing gasoline of increased octane number from a naphtha feedstock boiling within the range from about ll0F. to about 450F. (a clepentanized naphtha) and having a total C paraffin content of at least about 4 percent, a normal C paraffin content of at least about 3 percent and a ratio of iso-C paraffins to normal C paraffin within the range from about 1/3 to about 3/1.

The process comprises separatingthe naphtha feedstock by rough distillation into a first fraction boiling within the range from about 1 10F. to about 170F. and a second fraction boiling within the range from about 145F. to about 450F.

The first fraction is contacted with an adsorbent selective for adsorbing normal C paraffin in at least one of a plurality of selective adsorption zones. A light isoparaffin enriched fraction as described in embodiment lV above is recovered, said light iso-paraffin enriched fraction having a ratio of iso-C paraffins to normal C paraffin above the thermodynamic equilibrium ratio under the reforming zone conditions used for reforming a heavy fraction as set out below and having at least one-half of the total iso-C paraffins from the naphtha feedstock. The light isoparaffin enriched fraction is recovered from the contacting in at least one of a plurality of selective adsorption zones.

The contacting of the first fraction with the selective adsorbent is periodically discontinued when the ratio of iso-C paraffins to normal C paraffin in said light isoparaffins, naphthenes or benzene. A light isoparaffin enriched fraction is recovered from the adsorption zone, said light isoparaffin enriched fraction comprising said iso-C paraffins, naphthenes and benzene, if present, and said light isoparaffin enriched fraction having a ratio of iso-C; paraffins to normal C paraffins above the thermodynamic equilibrium ratio of iso-C paraffins to normal C paraffin under the conditions of the catalytic reforming of aheavy fraction as set out below and having at least one-half of the total iso-C paraftins from the naphtha feedstock. The contacting of the first fraction with the selective adsorbent is discontinued when the ratio of iso-C paraffins to normal C paraffin in said light isopara'ffin enriched fraction approaches or falls below the thermodynamic equilibrium ratio under the conditions of catalytic reforming of a heavy fraction as set' out below.

A normal C paraffin enriched stream is removed from the selective adsorbent and the contacting of the first fraction with the selective adsorbent is recommenced. The heavy fraction comprising. said second paraffin enriched fraction approaches or falls below the thermodynamic equilibrium ratio under the conditions of catalytic reforming of a heavy fraction as set out be.- low. Thereafter, or substantially simultaneously with the periodic discontinuing, the first fraction is contacted with the selective adsorbent in at least one other of said plurality of selectiveadsorption zones. A light isoparaffin enriched fraction is recovered from the contacting in said other selective adsorption zone, said light isoparafiin enriched fraction being as set out in the preceding paragraph.

A normal C paraffin stream is removed from the selective adsorbent in at least one of a plurality of selective adsorption zones which is no longer efficiently absorbing normal C paraffin. The heavy fraction comprising said second fraction and a normal C paraffin enriched stream removed from said selective adsorption zone, said heavy fraction having at least 60 percent, on the average, of the total normal C paraffin from said naphtha feedstock is contacted with hydrogen and a reforming catalyst in a reforming zone at reforming conditions. The reformate is combined with the light isoparaffin enriched fraction obtained from the plurality of selective adsorption zones to produce the product of increased octane number.

BRIEF DESCRIPTION OF THE DRAWINGS,-

FIG. 1 graphically presents data illustrating gasoline yield advantage which was found to be obtained by the process of the present invention.

FIG, 2 illustrates the invention broadly.

FIGS. 3, 4, and illustrate specific embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION The Naphtha Feedstock It is essential to the practice of the present invention that the naphtha feedstock used contain significant amounts of iso-C and normal C paraffins and it is especially preferred that the feedstock be selected from those naphtha feedstocks having a total C paraffin content of at least 4 volume percent, a normal C paraffin content of at least 3 volume percent, and a ratio of iso-C paraffins to normal C paraffin within the range from about 1/3 to about 3/1. Preferably, the naphtha feedstock, will have a total C paraffin content of at least 6 percent, and still more preferably of at least 8 percent. The normal C paraffin content of the naphtha feedstock when the total C paraffin content is at least 6 percent will preferably be at least 4 percent. The normal C paraffin content of the naphtha feedstock when the total C paraffin content thereof is at least 8 percent will preferably be at least 5 percent. More preferably, the volume ratio of iso-C paraffins to normal CG paraffin in the naphtha feedstock will fall withinthe range from about l/3'to about 2.5/l, and still more preferably within the range from about 1/2 to about 2/l. All of the percents and ratios mentioned in this specification with respect to feedstocks, fractions, streams and the like are volume percents and volume ratios, unless otherwise indicated.

The term iso-C paraffins as used herein includes the compounds 2,3-dimethyl butane, 2,2-dimethyl butane, 2-methyl pentane and 3-methyl pentane.

The following table is presented to further clarify the process of the invention. In the table the approximate boiling points and octane numbers of a number of C and C hydrocarbons are set out.

The selected naphtha feedstock will generally boil within the range from about 80 F. to about 450F. The feedstock can be. forexample, a straight-run naphtha, a coker naphtha, a thermally cracked or catalytically cracked naphtha, or blends thereof.

Separating the Feedstock It is essential to the practice of the invention that the naphtha feedstock described above be separated so as to produce a light isoparafiin enriched fraction, con- 8 taining at least one-half of the iso-C paraffins in the naphtha feedstock, and preferably having an iso-C paraffin to normal C paraffin ratio above the thermodynamic equilibrium ratio (TER) for iso-C paraffins to normal C paraffin under the conditions in the reforming zone (the refonning zone used for reforming the heavy fraction).

It is further essential to the invention that the heavy fraction contain at least 60 percent of the normal C paraffins in the naphtha feedstock, andpreferably having an iso-C paraffin to normal C paraffin ratio substantially below the TER for iso-C paraffins to normal C paraffin under the conditions in the reforming zone. The term substantially, as used with respect to the TER and the iso-C parafiins to normal C paraffin ratio in the heavy fraction, is used to indicate no more than about 60 percent of the TER, more preferably no more than about 40 percent of the TER, and most preferably no more than about 20 percent of the TER.

The TER at the conditions in the reforming zone, or for that matter at other conditions as well, can be calculatedby standard thermodynamics calculations from known free energy values (see, for example, The

Chemical Thermodynamics of OrganicCompounds by DR. Stull, E. F. Westrum, Jr., and G. C. Sinke, John Wiley, Inc., 1969).

In the broadest sense, the light isoparaffin enriched fraction may boil within the range from about F. to about 170F. and the heavy fraction may boil within the range from about F.. to about 450F. The rather large overlap in temperature, i.e., between 90F. and 170F., is not critical by itself so long as the ratios of iso-C paraffins to normal C paraffin in the light fraction and the heavy fraction and the amounts of iso-C paraffins and normal C paraffin are as specified herein.

In one embodiment of the invention, the separation can be accomplished using a distillation column, said distillation being operated with a cut point in the range from about F to about F .This will produce the light fraction having a boiling range from about 80F. to about l55F. and the heavy fraction having a boiling range from about 145F. to about 450F. The distillation column advantageously is a deisohexanizer,'i.e. a column which distills substantially all or at least most of the isohexane's overhead and leaves as the bottoms product material boiling at a higher temperature than the isohexanes.

By cut point temperature is meant the temperature which nominally separates the light fraction and the heavy fraction. The cut point temperature refers to the separation as if it takes place at atmospheric pressure, i.e., it is the temperature which nominally separates the light fraction and the heavy fraction at one atmosphere of pressure, although the distillation column may be operated at any convenient pressure which will facilitate the desired separation. Actually, of course, there is some overlap in the boiling ranges of the light and heavy fractions.

It is preferable that the light fraction have an iso-C paraffin to normal C paraffin ratio at least the TER under the conditions in the reforming zone.

The amounts and ratios of isoand normal C and C paraffins in the naphtha feedstock and the various fractions and streams separated therefrom can be readily determined by existing analytical techniques including, for example, gas chromatography. If desired, a device or devices utilizing an appropriate analytical technique the flow of a light fraction to a selective adsorption zone which is efficient in adsorbing normal C paraffin and normal C paraffin and away from a selective adsorption zone that is not sufficiently efficient in adsorbing normal C paraffin and normal C paraffin.

To accomplish the embodiment wherein a cut point in the range from about 145F. to about 155F. is used, it is preferred that a distillation apparatus providing at least about N theoretical plates be utilized. More preferably, at least about 1.5 times N, and still more preferably at least about 2 times N, theoretical plates are used. N is defined by the equation:

N Log tXm/X... na/ uil/ g (via/vi where X and X are the volume .fractions of the iso-C paraffins, Z-methylpentane and 3-methylp'entane, in the distillate and bottoms products, respectively, from the distillation zone,

X and X,,,, are the volume fractions of normal C paraffin in the distillate and bottoms products, respectively, from the distillation zone,

VP, is the volume'average vapor pressure of iso-C paraffins at the temperature of the distillation zone, and

VP, is the vapor pressure of normal C paraffin at the temperature of the distillation zone.

In another specific embodiment of the invention, the naphtha feedstock defined above is separated by rough distillation into a first fraction boiling within the range from about 80F. to about 170F. and a second fraction boiling within the range from about 145F. to about 450F. A cut point in the range from about l45F. to about 170F. in adistillation column is used to accomplish this separation.

The first fraction is contacted in an adsorption zone with an adsorbent that selectively adsorbs normal C paraffin, and normal C paraffin if present, from the feedstock without significantly adsorbing iso-C paraffins if present, iso-C paraffins, naphthenes, and benzene if present. The following discussion will assume the presence of C paraffin but as set out above, in some embodiments of the invention a depentanized feedstock l 10F.+) may be used. The iso-C paraffins, iso-C paraffins, naphthenes and benzene if present are recovered from the adsorption zone as a light isoparaf fin enriched fraction having a ratio of iso-C paraffins to normal C paraffin above the TER of iso-C paraffins to normal C paraffin under the conditions of the catalytic reforming zone (wherethe heavy fraction is reformed).

The contacting of the first fraction with the selective adsorbent is discontinued when the selective adsorbent is no longer adsorbing sufficient normal C and normal paraffins to provide the essential ratio of iso-C paraffins to normal C, paraffin above the TER of iso-C paraffins to normal C paraffin under the conditions of the catalytic reforming zone.

The normal C paraffin and normal C paraffin are then removed from the selective adsorbent, after when the contacting of the first fraction with the selective adsorbent is recommenced. A heavy fraction, comprising the second fraction and a normal C paraffin and normal C paraffin-enriched stream generally boiling within the range from about 90F to about l60F. removed from the selective adsorbent, is contacted with hydrogen and a reforming catalyst at reforming condi-- 1 tions in a reforming zone. The heavy fraction has a ratio of iso-C parafiins to normal C paraffin below the TER of iso-C paraffins to normal C paraffin under the conditions of the reforming zone and has at least 60 percent of the total normal C paraffin from the naphtha feedstock. The reformate from the reforming zone is combined with the light isoparaffin enriched fraction to produce the product of increased octane number.

The adsorbent which selectively adsorbs normal C and normal C paraffins without significantly adsorbing iso-C paraffins, iso-C paraffins, naphthenes and benzene,'if present, is generally a porous solid material having pores or slit-like (rectangular) openings, hereafter collectively referred to as pores, of substantially uniform size. Preferably the porous solid material has pores of a size (the short side of rectangular openings or the diameter of the pore if the pore is considered for convenience to be circular in cross-section) within the range from about 4 Angstroms to about 7 Angstroms. More preferably, the porous solid material has pores of a size in the range from about 4.5 Angstroms to about 6 Angstroms. Typical useful porous solid materials are crystalline zeolitic molecular sieves or porous carbons manufactured to have pores of substantially uniform size. Both of such materials are commercially available. The precise chemical nature of the porous solid material is, however, not of great importance so long as it is not such as to cause significant decomposition or other deterioration of the first fraction under the conditions existing in the adsorption zone.

The normal C paraffinand normal C paraffin-enriched stream, which generally boils within the range from about 90F. to about 160F., may be removed from the selective adsorbent by, for example, heating said selective adsorbent, depressuring said selective adsorbent, displacing the normal C and C paraffins .by other adsorbable compounds, or flushing said selective adsorbent with an inert gas or hydrogen, etc. or combination thereof. Methods of operating selective adsorption zones are well known in the prior art, do not form a part of the present invention and, hence, will not be discussed in greater detail herein.

Generally, the nonnal C paraffinplus normal C paraffin-enriched stream removed from the selective adsorbent will boil within the range from about 90F to about 160F. Thus, the heavy fraction, which comprises the second fraction and the normal C paraffinand normal C paraffin-enriched stream removed from the selective adsorbent, will generally boil within the range from about 90F. to about 450F. The light isoparaffin enriched fraction, which comprises the iso-C paraffins, iso-C parafiins, naphthenes and benzene if present, will generally boil within the range from about 80 F. to about lF.

Still another embodiment of the invention utilizes rough distillation in a distillation column which separates the naphtha feedstock set out above into a first fraction boiling within the range from about F. to about 170F. and a second fraction boiling within the range from about F. to about 450F. The separatin g is accomplished generally by using a distillation column operating with a cut point in the range from about 145F. to about 170F. if desired, a depentanized 1 F.+) feedstock may be employed.

The first fraction is contacted with an adsorbent selected for adsorbing normal C paraffin and normal C paraffin in at least one of a plurality of selective adsorption zones. A stream enriched in iso-C paraffins, iso-C paraffins, naphthenes and benzene, if present, is recovered as a light isoparaffin enriched fraction having a ratio of iso-C paraffins to normal C paraffin above the TER of iso-C paraffins to normal C paraffin under the reforming conditions used for reforming a heavy fraction as described below. The contacting of the first fraction with the selective adsorbent in said at least one of a plurality of selective adsorption zones is discontinued when the ratio of iso-C paraffins to normal C paraffin in the light stream enriched in iso-C paraffins, iso-C paraffins, naphthenes and benzene, if present, is no longer sufficiently above the TER in the reforming zone. Thereafter or substantially simultaneously with discontinuing the contacting of the first fraction with the selective adsorbent in the zone which has become insufficiently efficient in adsorbing normal C paraffin and normal C paraffin, the first fraction is contacted with the selective adsorbent in at least one other of said plurality of selective adsorption zones.

A stream enriched in iso-C paraffins, iso-C paraffins, naphthenes and benzene, if present, is then recovered as the light isoparaffin enriched fraction from said contacting in said other selective adsorption zone. Said light isoparaffin enriched fraction has a ratio of iso-C paraffins to normal C paraffin above the TER of iso-C paraffins to normal C paraffin under the reforming zone conditions and has at least one-half of the total iso-C paraffinsfrom the naphtha feedstock.

A normal C paraffinand normal C paraffin-enriched stream is removed from the selective adsorbent in at least one of a plurality of selective adsorption zones wherein the contacting has been discontinued. A heavy fraction comprising the second fraction and the normal C paraffinand normal C paraffin-enriched stream removed from the selective adsorption zone is contacted with hydrogen and a reforming catalyst in a reforming zone at reforming conditions and the reformate is combined with the light isoparaffin enriched fraction obtained from the plurality of selective adsorption zones to produce the product of increased octane number.

When the separation process comprises distillation with a cut point in the range from [45F to 170F plus selective adsorption of the normal C paraffin and normal C paraffin in the 80F. to 170F. fraction as described in the last two embodiments above, it is necessary that the cut point between the first (80l70F.) fraction and the second 145450F.) fraction be precise enough to achieve a reasonable degree of separation between the iso-C paraffins, which are preferably not reformed, and cyclohexane, which is preferably reformed. Generally it is desirable that the distillation be performed in an apparatus providing at least 1.5 N theoretical plates. N is defined by the equation:

Where X and X are volume fractions of the iso-C paraffins, Z-methylpentane and 3-methylpentane, in the distillate and bottoms products, respectively, from the distillation zone,

X and X are volume fractions of cyclohexane in the distillate and bottoms products, respectively, from the distillation zone, 1

VP,- is the volume average vapor pressure of iso-C paraffins at the temperature of the distillation zone, and

VP is the vapor pressure of cyclohexane at the temperature of the distillation zone.

It is, of course, understood that this is only an approximate equation and that the critically determining factor is that the ratio of iso-C paraffins to normal C paraffin in the light isoparaffin enriched fraction be as critically required above, that the ratio of iso-C paraffins to normal C paraffin in the heavy fraction be as critically defined above, and that the amounts of iso-C paraffins and normal C paraffin in the light isoparaffin enriched stream and heavy fraction be above.

Reforming Catalyst The catalyst used in the reforming zone-will generally comprise a porous solid carrier support, such as alumina upon which catalytically active amounts of a platinum group component are included. Generally, a halogen component is also'included upon the porous solid carrier. 1

The reforming catalyst can also contain promoter components which improve the activity, fouling rate, stability and/or selectivity of the platinum-alumina catalyst. Typical promoting agents include rhenium, germanium, tin, lead, and technetium. The platinum group component should be present in an amount from 0.01 to 5 weight percent, preferably from 0.01 to 3 weight percent calculated as the metal based on'the finished catalyst.

The promoter component, when a promoter component is used as a part of the catalyst, is preferably present in an amount from about 0.01 to 5 weight percent calculated as the metal based on the finished catalyst.

Reforming Conditions Reforming conditions will depend on a large measure on the feed used,whether aromatic, paraffinic, or naphthenic, and upon the desired octane rating of the product, said feed being limited to those feeds described above as suitable to the practice of the present invention. The temperature in the reforming process will generally be in the range from about 600F. to about 1100F. and preferably from about 700F. to about 1050F. The pressure in the reforming zone can be atmospheric or super atmospheric. The pressure will generally lie within the range from about 25 to about 1,000psig, preferably from about 50 to about 750 psig and more preferably, when a promoter component is present in the reforming catalyst, from about 50 to about 300 psig. The temperature and pressure can be correlated with the liquid hourly space velocity (LHSV) to fabor any particularly desirable reforming reaction as, for example, dehydrocyclization, isomerization or cracking. Generally the liquid hourly space velocity will be from 0.1 to about 10 and preferably from about 1 to about 5.

Reforming of a naphtha is accomplished by contacting the naphtha at reforming conditions and in the presas critically defined ence of hydrogen with the desired catalyst. Reforming generally results in the production of hydrogen. The hydrogen produced during the reforming process is generally recovered from the reaction product and preferably at least part of said hydrogen is recycled to the reaction zone. Thus, excess or make-up hydrogen need not necessarily be added to the reforming process although it is sometimes preferred to introduce excess hydrogen at some stage of the operation, for example, during startup. Hydrogen either as recycle or make-up hydrogen can be added to the feed prior to contact with the catalyst or can be contacted simultaneously with the introduction of feed to the reaction zone. Hydrogen is preferably introduced into the reforming zone at a rate from about 0.5 to about 20 moles of hydrogen per mole of feed. The hydrogen can be in admixture with light gaseous hydrocarbons.

DETAILED DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to FIG. 1 and to the specific embodiments illustrated in FIGS. 2-5.

FIG. lshows the overall blend yield of C liquid of a given octane for three different reforming cases: 120F.+ feed to reforming; 150F.+ feed. In all three cases the naphtha feed was split into a heavy fraction and a light fraction, the heavy fraction fed to reforming, and the resulting stabilized reformate was blended with the light fraction to obtain the final overall blend. The yield of overall blend as liquid volume percent of the uncut total naphtha feedstock is the ordinate of FIG. 1. The overall blend octane is the abscissa of FIG. I. For a given case, e.g. where the reformer feed was 180F.+. various overall blend octanes were experimentally established by running a reforming unit at various severities to thereby vary the octane of the reformate product. The operating conditions can be summarized as follows:

Naphtha feedstock: Arabian light naphtha; boiling range C;,-280F.; iso-C paraffin content. 8.8 per cent; normal C paraffin content. I 1.9 percent.

The naphtha feedstock was split to give:

least 4 volume percent, a normal C paraffin content of at least 3 volume percent, and a ratio of iso-C paraffins to normal C paraffin within the range from about l/3 to about 3/1 is introduced via line 1 into Separator 2. If desired a depentanized naphtha feedstock boiling in the range 1 F. to 450F. may be used. A light fraction having an iso-C paraffin to normal C paraffin ratio greater than two-thirds the TER, and preferably above the TER under the conditions in Catalytic Reformer 5 for iso-C paraffins to normal C paraffin in Catalytic Reformer 5, and having at least one-half of the iso-C paraffins from the naphtha feedstock is removed from the Separator 2 via Line 3. A heavy fraction having an iso-C paraffin to normal C paraffin ratio substantially below the TER, and preferably less than one-third of the TER, under the conditions in the Catalytic Reformer 5 for lSO-Cr; paraffins to nonnal C paraffin and having at least 60 percent of the normal C paraffin from the naphtha feedstock is removed from the Separator 2 via Line 4 and introduced into Catalytic Reformer 5. Hydrogen is introduced into Catalytic Reformer 5 via Line 6. A mixture of hydrogen-and the catalytic reformate is conducted via Line 7 from Catalytic Reformer 5 to Vapor-Liquid Separator 8. Recycle hydrogen is conducted via Line 9 from Vapor-liquid Separator 8 to the Catalytic Reformer 5. The catalytic reformate is conducted via Line 10 from the Vapor- Liquid Separator 8 into Stabilizer ll (debutanizer) and from Stabilizer 11 via Line 12 intocombination with:

the light fraction of Line 3 to form' gasoline or a gasoline blending stock. C C hydrocarbons are removed from Stabilizer 11 via Line 13.

3. A heavy fraction boiling within the range from about 145F. to about 450F. is removed from Distillation 0 Zone via Line 4. The heavy fraction is treated in conformance with the description of FIG. 2.

Heavy Fraction Light Fraction Reforming temperature: 875-950F. Reforming pressure: 200 psig total Reforming catalyst: platinum-rhenium on chlorided alumina Reforming liquid hourly space velocity: 1.3 Reforming feed, hydrogen to hydrocarbon ratio: 4

As can be seen by the graphical presentation of the data in FIG. 1, the case where the normal C paraffin, iso-C paraffin lean. 150F.+ material was fed to the reformer was discovered to give the highest overall blend yield for any given overall blend octane number. This is shown by the top curve in FIG. 1 which is the curve for feeding 150F.+ material (with the prerequisite amount of normal C paraffin and relative absence of iso-C paraffin).

Referring now to FIG. 2, a naphtha feedstock boiling within the range from about 80 F. to about 450F., said naphtha feedstock having a C paraffin content of at FIG. 4illustrates another specific embodiment of the invention. The naphtha feedstock previously described is introduced via Line 1 into Distillation Zone 30. A first fraction boiling within the range from about F. to about 170F. is conducted from Distillation Zone 30 via Line 31 to Selective Adsorption Zone 32. A second fraction boiling within the range from about F. to about 450F. is conducted from Distillation Zone 30 via Line 34. A light isoparafiin enriched fraction boiling within the range from about 80F. to about F., having an iso-C paraffin to normal C paraffin ratio above the TER, and having at least one-half of the iso-C paraffins from the naphtha feedstock is removed from Selective Adsorption Zone 32 via Line 3. When the ratio of iso-C paraffins to normal C paraffin in the light iso-paraffin enriched fraction approaches or falls below the TER, the contacting of the first fraction with the selective adsorption material in the Selective Adsorption Zone 32 is discontinued and the adsorbed normal C paraffin and normal C paraffin are removed from the selective adsorbent within the Selective Adsorption Zone 32 via Line 33. The second (145F.-450F.) fraction and the normal C paraffin and normal C paraffin-enriched stream from the selective adsorbent can then be combined via Line 4 and further processed as the heavy fraction of FIG. 2 or the second fraction and the normal C paraffinand normal C paraffin-enriched stream may be introduced separately into the Catalytic Reformer 5 of FIG. 2 and thereafter treated as described in FIG. 2. After the normal C paraffinand normal C paraffin-enriched stream has been removed from the selective adsorbent in the Selective Adsorption Zone 32, the contacting of the first (80F-170F.) fraction with the selective adsorbent in Selective Adsorption Zone 32 is recommenced.

FIG. 5 illustrates still another specific embodiment of the present invention wherein the naphtha feedstock previously described is introduced via Line 1 into Distillation Zone 30. A first fraction boiling within the range from about 80F. to about 170F. is conducted via Line 31 to Flow Director 40. Flow Director 40 controls the flow of the first fraction either via Line 41 to Selective Adsorption Zone 42 or via Line 51 to Selective Adsorption Zone 52. For the purposes of description it will be assumed that the flow of the first fraction is directed to Selective Adsorption Zone 42 via Line 41. In Selective Adsorption Zone 42 the first fraction contacts a selective adsorbent which will adsorb normal C paraffin and normal C paraffin, but will not adsorb iso-C paraffins. iso-C paraffins, naphthenes, or benzene. A stream enriched in iso-C paraffins, iso-C paraffins naphthenes and benzene if present is removed as a light isoparaffin enriched fraction from Selective Adsorption Zone 42 via Line 43. The ratio of iso-C paraffins to normal C paraffin in the light isoparaffin enriched fraction is above the TER and the light isoparaffin enriched fraction has at least one-half of the total iso-C paraffins from the naphtha feedstock. As the ratio of iso-C paraffins to normal C paraffin towards the TER, i.e., as the selective adsorbent in Selective Adsorption Zone 42 starts to become substantially saturated with normal C paraffin and normal C paraffin, the Flow Selector 40 stops the flow of the first fraction via Line 41 and directs its flow via Line 51 to Selective Adsorption Zone 52. Selective Adsorption Zone 52 operates in exactly the same manner as Selective Adsorption Zone 42 to produce the light isoparaffin enriched fraction which is removed from Selective Adsorption Zone 52 via Line 53. The light isoparaffin enriched fraction. whether it comes from Selective Adsorption Zone 42 or Selective Adsorption Zone 52 proceeds via Line 43 or 53 and Line 3 to the combining as described with respect to FIG. 2. The normal C paraffin and normal C paraffin adsorbed on the selective adsorbent in Selective Adsorption Zone 42 are removed as a normal C paraffinand normal C paraffin-enriched stream from said selective adsorbent in Selective Adsorption Zone 42 via line 44 and along with the second 145F. 450F.) fraction coming from the Distillation Zone 30 via Line 34 are passed via Line 4 as a heavy fraction to the Reformer Sand the subsequent processing as described in FIG. 2. Altematively, of course, the second (145F. -450F.) fraction may be passed via Line 34 directly to the Catalytic Re former 5 and the normal C parafiinand normal C paraffin-enriched stream may be passed directly via Line 44 to the Catalytic Reformer 5. When the ratio of iso-C paraffins to normal C paraffin in the light isoparaffin enriched fraction being removed fromSelective Adsorption ZOne 52 via Line 53 begins to fall towards the TER, the Flow Selector 40 switches once again to direct the flow of the first (80F -1 F.) fraction via line 41 instead of Line 51.

The specific embodiment of FIG. 3 shows two selective adsorption zones. It is, of course, possible to have more than two selective adsorption zones in which case the Flow Selector 40 will operate to direct flow of the first fraction to a selective adsorption zone that produces a light isoparaffin enriched fraction having an iso-C paraffin to normal C paraffin ratio well above the TER while normal C paraffin and normal C paraffin are being removed from selective adsorption zones which have become substantially saturated therewith. Thus, while the embodiment specifically illustrated in FIG. 5 shows two selective adsorption zones, a plurality of selective adsorption zones is clearly contemplated as falling within the scope of the invention.

The invention will be better understood by reference to the illustrative examples which follow:

EXAMPLE 1 Portions of naphtha feedstock boiling within the range from about F to about 280F., said naphtha feedstock having 21 volume percent C paraffins, of which 12 volume percent were normal C paraffin and having a ratio of iso-C paraffins to normal C paraffin of about 3/4 was used in two processes as described below. While the exact amount of naphtha treated in each process was other than 1,000 barrels, the processes are described on a 1,000-barrel level to make them more easily comparable.

Process 1, which was not performed according to the teachings of the present invention, was performed as follows. one thousand barrels of the naphtha feedstock was distilled using a cut point of 180F. into a light fraction and a heavy fraction. The light fraction consisted of approximately 440 barrels and had an F1 clear octane number of 62.2. The heavy fraction which consisted of approximately 560 barrels was reformed in a catalytic reformer, the catalytic reformer operating at a pressure of 200 psig, a liquid hourly space velocity of 1.3, and with a hydrogen-to-hydrocarbon mole ratio of 4.0. The catalyst used in the catalytic reformer comprised 0.3 weight percent platinum, 0.2 weight percent rhenium, 0.4 weight percent tin and 1.1 weight percent chlorine on an alumina support. 379 barrels of reformate having an F1 clear octane rating of 101.3 was obtained from the catalytic reformer. The reformate was combined with the light fraction. The F-l clear octane number of the blend was measured and found to be 82.5. The total number of barrels obtained from Pro cess l was 440 barrels from the light fraction plug 379 barrels from the reformate for a total of 819 barrels.

Process 2, which was a process performed in accordance with the invention, and more specifically in accordance with FIG. 3 was performed as follows. One thousand barrels of the same naphtha feedstock as was used in Process 1 was separated in a distillation zone using a cut point of F. A light isoparaffin enriched fraction containing approximately 280 barrels and having an F-l clear octane of 72 was obtained. A heavy fraction of approximately 720 barrels was reformed in a catalytic reformer operating at a pressure of 200 psig, a hydrogen-to-hydrocarbon mole ratio of 4.0, and a liquid hourly space velocity of 1.3. The catalyst used in the catalytic reformer was the same catalyst as was used in Process 1. Approximately 536 barrels of reformate having F-l clear octane number of 92.0 was obtained. The reformate and the light fraction were combined to form a gasoline pool. The F-l clear octane number of the blend was measured and found to be 85.3. The total product produced by Process 2 was 280 536 816 barrels.

Thus, Process 1, which was not a process operated in accordance with the invention, produced 819 barrels of 81 F-l clear octane product, whereas Process 2, which was a process of the present invention, produced 816 barrels of 85.3 F-'1 clear octane number product.

A very significant increase of 2.8 F-l clear octane numbers resulted from using the process of the present invention.

EXAMPLE 2 The measured points in FIG. 1 were generated by substantially the same procedure as used for Processes l and 2 of Example 1. The l50F.-lcurve of FIG. 1 was generated in accordance with the present invention;

the l20F.+ and the 180F.+ curves were not generated in accordance with the present invention. Comparison of the l50F.+ curve to the other curves shows:

a. The present invention gives a higher overall blend yield at a given blend octane or b. A higher blend octane at a given overall blend yield.

Although the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses or adaptations of the invention following,'in general, the principle of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains.

What is claimed is:

1. A process for producing a high overall blended yield of gasoline at a given octane-which comprises a. separating a naphtha feedstock which contains iso-C, and normal C paraffins into a light fraction containing at least one-half of the total iso-C paraffins and a heavy fraction containing at least 60 percent of the normal C parafiin, and wherein the separating of said light and heavy fractions comprises fractionating said naphtha feedstock at a cut point within the range from about l45F. to about l55F.. amd so that the heavy fraction is substantially free of C paraffins,

b. catalytically reforming the heavy fraction to obtain reformate, and

(3. directly blending at least a portion of the light fraction with the reformate to obtain gasoline or gasoline blending stock.

2. A process as in claim 1, wherein the separation of the heavy fraction from the light fraction is carried out so that the heavy fraction has an iso-C paraffin to normal C paraffin ratio about one-third or less of the thermodynamic equilibrium ratio under the conditions in the reforming zone, and the light fraction has an iso-C,

18 paraffin to normal C paraffin ratio more than about twothirds of the thermodynamic equilibrium ratio under the conditions in the reforming zone.

3. A process as in claim 2, wherein the naphtha feedstock boils within the range of about 450F. and

has a total C paraffin content of at least 4 volume 'per- V cent, a normal'C paraffin content of at least 3 volume percent, and a ratio of iso-C paraffins to nonnal C paraffin within the range from about 1/3 to about 3/1.

4. A process as in claim 3, herein the separation of said light and heavy fractions comprises fractionating said naphtha feedstock boiling at a cut point within the range from about l45F. to about 155F., wherein said light isoparaffin-enriched fraction boils within the range from about 80F. to about 155F. and wherein said heavy fraction boils within the range from about F. to about 450F.

5. A process in accordance with claim 2, wherein the separation is carried out so that the ratio of iso-C paraffins to normal C paraffin in said heavy fraction is no more than about 20 percent of the thermodynamic equilibrium ratio under the conditions in the reforming zone.

6. A process in accordance withfclaim 4, wherein the fractionating is carried out by distillation in a distillation apparatus providing at least about l.5 N theoretical plates. said N being defined by the equation:

where I X and X are the volume fractions of the iso-C paraffins, Z-methylpentane and 3-methylpentane, in the distillate, and bottoms products, respectively, from the distillation zone,

X and X,,,, are the volume fractions of normal C paraffin in the distillate and bottoms products, respectively, from the distillation zone,

VP,- is the volume average vapor pressure of iso-C paraffins at the temperature of the distillation zone, and

VP is the vapor pressure of normal C paraffin atthe temperature of the distillation zone.

7. A process as in claim 6, wherein the number of theoretical plates is at least about 2.0 N. v

8. A process which comprises:

a. separating a naphtha feedstock which boils within the range of about 80-450F. and has a total C paraffin content of at least 4 volume percent, a normal C paraffin content of at least 3 volume percent, and a ratio of iso-C paraffins to normal C paraffin within the range from about l/3 to 3/1 by distillation into a first fraction boiling within the range from about 80F. to about l55F. and a second fraction boiling within the range from about 145F. to about 450F. so that the second fraction has an iso-C paraffin to normal C parafiin ratio about one-third-or less of the thermodynamic equilibrium ratio under the conditions in the reforming zone. and the first fraction has an iso-C paraffin to normal C paraffin ratio more than about twothirds of the thermodynamic equilibrium ratio under the conditions in the reforming zone,

b. contacting said first fraction in an adsorption zone with an adsorbent that selectively adsorbs normal C and normal C paraffins without significantly adsorbing iso-C paraffins, or naphthenes,

c. recovering from said adsorption zone said iso-C paraffins, iso-C paraffins and naphthenes as a light isoparaffin-enriched fraction (i) having a ratio of 5 iso-C paraffins to normal C paraffin above the thermodynamic equilibrium ratio under the conditions of the catalytic reforming zone of step (e), and (ii) having at least one-half of the total iso-C parafflns from the naphtha feedstock,

d. recovering a normal C paraffinand normal C paraffin-enriched stream from said selective adsorbent;

e. contacting a heavy fraction comprising said second combining the reformate with the light isoparaffinenriched fraction to produce a gasoline or gasoline blending stock.

22 UNITED STATES PATENT OFFICE CERTIFXCATE 0F CORRECTION Patent No. ,10 Dated June 28 197 fl Thomas R. Hughes Robert L. Jacobson and Richard C. Robinson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Title Page, "T. G. DeJonghi" should read -T. G. DeJonghe-. Col. 3, line 27, "feestock" should read --feedstock-.

Col. lines 21-22, "one-half half of" should read -one-half of-.

Col. 5, line 52, "iso-Cg" should read --iso-'-C Col. 5, line- 52, "paraffins" 2nd ooo. should read paraffin-- Col. 8, line 39, "distillation being" should read -dlstillation column being-.

Q01. 9, line 67, "when" should read which. Col. 12, line 61, "fabor" should read --favor-.

Col, 13, line 2 "l50F.+ feed." should read -l50F.+ feed;

feed--- Col. 15, lines +2- +3, "paraffin towards" should read --p'araffin lowers towards.

Col. 16, line 6, "Zone" should read --Zone-.

Col 16, line 10, "FIG. 3" should read -FIG.-

Col. 16, line #1, "one" should read One-.

Col. 16, line 59, "plug" should read plus--. Claim 4, line 1, "herein" should read --wherein--.

Claim 8 last line under "b. "isoC paraffins or naphthenes,"

should read --iso-C paraffins, iso-C paraffins, or napht enes,--.

S'gned and sealed this 8th day of October 1974.

GIBSON JR. C. MARSHALL DANN Commissioner of Patents MCCOY M. Attesting Officer 

2. A process as in claim 1, wherein the separation of the heavy fraction from the light fraction is carried out so that the heavy fraction has an iso-C6 paraffin to normal C6 paraffin ratio about one-third or less of the thermodynamic equilibrium ratio under the conditions in the reforming zone, and the light fraction has an iso-C6 paraffin to normal C6 paraffin ratio more than about two-thirds of the thermodynamic equilibrium ratio under the conditions in the reforming zone.
 3. A process as in claim 2, wherein the naphtha feedstock boils within the range of about 80*-450*F. and has a total C6 paraffin content of at least 4 volume percent, a normal C6 paraffin content of at least 3 volume percent, and a ratio of iso-C6 paraffins to normal C6 paraffin within the range from about 1/3 to about 3/1.
 4. A process as in claim 3, herein the separation of said light and heavy fractions comprises fractionating said naphtha feedstock boiling at a cut point within the range from about 145*F. to about 155*F., wherein said light isoparaffin-enriched fraction boils within the range from about 80*F. to about 155*F. and wherein said heavy fraction boils within the range from about 145*F. to about 450*F.
 5. A process in accordance with claim 2, wherein the separation is carried out so that the ratio of iso-C6 paraffins to normal C6 paraffin in said heavy fraction is no more than about 20 percent of the thermodynamic equilibrium ratio under the conditions in the reforming zone.
 6. A process in accordance with claim 4, wherein the fractionating is carried out by distillation in a distillation apparatus providing at least about 1.5 N theoretical plates, said N being defined by the equation: N Log (XiD/XnD X XnB/XiB )/Log (VPi/VPn) where XiD and XiB are the volume fractions of the iso-C6 paraffins, 2-methylpentane and 3-methylpentane, in the distillate and bottoms products, respectively, from the distillation zone, XnD and XnB are the volume fractions of normal C6 paraffin in the distillate and bottoms products, respectively, from the distillation zone, VPi is the volume average vapor pressure of iso-C6 paraffins at the temperature of the distillation zone, and VPn is the vapor pressure of normal C6 paraffin at the temperature of the distillation zone.
 7. A process as in claim 6, wherein the number of theoretical plates is at least about 2.0 N.
 8. A process which comprises: a. separating a naphtha feedstock which boils within the range of about 80*-450*F. and has a total C6 paraffin content of at least 4 volume percent, a normal C6 paraffin content of at least 3 volume percent, and a ratio of iso-C6 paraffins to normal C6 paraffin within the range from about 1/3 to 3/1 by distillation into a first fraction boiling within the range from about 80*F. to about 155*F. and a second fraction boiling within the range from about 145*F. to about 450*F. so that the second fraction has an iso-C6 paraffin to normal C6 paraffin ratio about one-third or less of the thermodynamic equilibrium ratio under the conditions in the reforming zone, and the first fraction has an iso-C6 paraffin to normal C6 paraffin ratio more than about two-thirds of the thermodynamic equilibrium ratio under the conditions in the reforming zone, b. contacting said first fraction in an adsorption zone with an adsorbent that selectively adsorbs normal C5 and normal C6 paraffins without significantly adsorbing iso-C5 paraffins, or naphthenes, c. recovering from said adsorption zone said iso-C5 paraffins, iso-C6 paraffins and naphthenes as a Light isoparaffin-enriched fraction (i) having a ratio of iso-C6 paraffins to normal C6 paraffin above the thermodynamic equilibrium ratio under the conditions of the catalytic reforming zone of step (e), and (ii) having at least one-half of the total iso-C6 paraffins from the naphtha feedstock, d. recovering a normal C5 paraffin- and normal C6 paraffin-enriched stream from said selective adsorbent; e. contacting a heavy fraction comprising said second fraction and said normal C5 paraffin- and normal C6 paraffin-enriched stream with hydrogen and a reforming catalyst at reforming conditions in a reforming zone, said heavy fraction (i) having a ratio of iso-C5 paraffins to normal C6 paraffin substantially below the thermodynamic equilibrium ratio under the conditions of the reforming zone and (ii) having at least 60 percent of the total normal C6 paraffin content from the naphtha feedstock, and f. combining the reformate with the light isoparaffin-enriched fraction to produce a gasoline or gasoline blending stock. 